1. Field of the Invention
The present invention relates to a radio quality estimation system, a base station, a mobile station, and a radio quality estimation method for estimating a radio quality of a predetermined measurement period.
2. Description of the Related Art
In a radio communication system, since a propagation environment considerably fluctuates due to influence of fading, there have been applied thereto a transmission power control technique, an adaptive modulation and coding technique and the like. By the transmission power control technique, a transmission power is controlled pursuant to fluctuations in the propagation environment, and by the adaptive modulation and coding technique, transmission formats including a modulation scheme and a coding ratio and the like are controlled pursuant to fluctuations in the propagation environment due to fading. In techniques such as the transmission power control technique and the adaptive modulation and coding technique, it is required to estimate a radio quality in the propagation environment on the receiver side or the transmitter side, for the purpose of estimating fluctuations in a propagation environment. Here, the radio quality corresponds to a signal-to-interference ratio (SIR), a carrier-to-interference ratio (CIR), a channel quality indicator (CQI), or the like.
On the other hand, with regards to standardization of the third generation mobile communication system which is so-called the IMT-2000, a W-CDMA method has been developed by the 3GPP (Third-Generation Partnership Project) constituted of regional standardization organizations and the like, and standard specifications of cdma2000 have been developed by the 3GPP2 (Third-Generation Partnership Project 2). With the rapid popularization of the Internet in recent years, it is expected that high-speed and high-volume traffic by such causes as downloads from databases or websites will increase especially in downlinks. Therefore, in the 3GPP, standardization of the “High-speed Downlink Packet Access (HSDPA)”, which is a high-speed packet transmission method for a downlink, has been conducted (for example, refer to 3GPP TR25.848 V4.0.0). Also in the 3GPP2, standardization of the “1xEV-DO,” which is a transmission method dedicated for high-speed data in a downlink, has been conducted (for example, refer to 3GPP2 C.S0024 Rev.1.0.0). Note that “DO” in the 1xEV-DO means “Data Only.”
For example, in the HSDPA, a mobile station uses the CQI as control information for noticing a radio condition in a downlink. The CQI is calculated by the mobile station, based on the SIR obtained by using signals of a common pilot channel (CPICH), i.e., pilot signals, in the downlink. Additionally, the SIR is used, for example, in communication methods in the 3GPP other than the HSDPA, and other communication methods such as the cdma2000 method in the 3GPP2 and a TDD method. Accordingly, in each of these communication methods, it is preferable to estimate the SIR accurately in a measurement period defined in a specification thereof as a measurement period for estimating the SIR.